After repeated use, a station which is an aligning guide for a toolholder on a turret table, becomes enlarged, causing the tool holder to be relatively loosely guided and poorly aligned. Poor alignment of the toolholder results in destructive contact between the associated tool and die in a punching operation and ultimate battering and destruction of the tool and die.
Due to the expense of the tooling and difficulty of replacement of such stations and guides on the turret, it is highly desirable to restore the station without replacing or changing the toolholder or dismantling and reboring. However, any such restoration must provide new controlling surfaces between the toolholder and the station to protect the tool and die from misguided contact.
Two somewhat different methods for refurbishing a station are disclosed in U.S. Pat. Nos. 4,240,314 (Teeslink) and 4,756,630 (Teeslink). As described in U.S. Pat. No. 4,756,630, the method of U.S. Pat. 4,240,314 involves the drilling of spaced side bores in the toolholder wall and the insertion of plugs of resilient material into the bores to position the toolholder away from the wall of the station. The plugs extend outwardly into the toolholder bore sufficiently so that the toolholder compresses the resilient plugs tightly into the side bores. The toolholder reciprocates across ends of the plugs. The small plugs provide limited bearing surface and wear soon occurs requiring the replacement of the plugs, although their resilient spring back extends the useful life somewhat. The plastic tends to creep under constantly applied load so that the advantage of the compression is largely lost. This method is therefore of severely limited value, either for repair or for original equipment.
U.S. Pat. No. 4,756,630 endeavors to ameliorate the application of spaced supports within a station by replacing spaced plugs with longitudinal wear strips. The wear strips are retained within keyways machined in the sides of a refurbished station. To be effective, toolholder bearing surfaces of the strips must provide close but clearing surfaces which are symmetrically disposed about the longitudinal axis of the toolholder. Preferably, the strips and keyways are dovetailed. Keyways are taught to be provided by broaching the cylindrical walls of the station using special tools, in a first step as a rectangular keyway and in a second step as a dovetail using a dovetail shaped broach. To make matching strips, rectangular blanks of plastic bearing material are forcibly intruded lengthwise into the dovetail thereby removing excess material and forcing the strip to fit. Finally the radially protruding strip is formed by longitudinal broaching. While no dismantling of an associated turret is required, the process requires a plurality of high precision and involved steps and specialized tooling as recited above to refurbish a station.